1. Field of the Invention
The present invention relates to an image processing apparatus, and in particular, an image processing apparatus for correcting an image signal having a defect caused by a pixel defect existing in an image sensor.
Priority is claimed on Japanese Patent Application No. 2005-318120, filed Nov. 1, 2005, the content of which is incorporated herein by reference.
2. Description of the Related Art
In image input apparatuses such as video cameras or digital cameras, a zoom function is widely used for freely expanding or contracting the image in accordance with the distance to a subject to be photographed, or the size of the subject in the angular field. The zoom function is classified into: (i) optical zooming generally implemented by mechanically moving internal lenses, and (ii) electronic zooming for performing image expansion by using a part of the image output from the image sensor and interpolating new pixels between existing pixels so as to generate an interpolated image. In comparison with the optical zooming, the electronic zooming includes no elements to be driven, and can be realized as a small device at low cost; however, image quality thereof is inferior.
With respect to such a problem, Japanese Unexamined Patent Application, First Publication No. H10-233950 discloses an electronic zoom image input system having: a fixed-focal-length image input optical system for compressing a periphery of an input image; and a light receiving element, having a substantially uniform pixel density, for photo-detecting the input image. This electronic zoom image input system has a function of correcting and converting the image which is detected by the light receiving element and includes distortion due to the above compression, thereby producing a zoom image of high quality. In accordance with this system, for both wide-area imaging and telephoto imaging, it is possible to obtain an image in which the central part is less degraded while degradation of the peripheral part is inevitable.
As the image sensor in a video camera or a digital camera, a CMOS (complementary MOS) image sensor or a CCD (charge coupled device) image sensor is popularly used. Such an image sensor may include dust particles in a manufacturing process, or may be affected by radiation after manufacturing, which may cause defect pixels appearing when there is excessive dark current, abnormal signal readout from the pixels, excessive insufficiency of pixel sensitivity, or the like. Conventionally, when such defect pixels are produced, they are corrected by linear interpolation using peripheral pixels around each defect pixel.